The present invention is directed to an apparatus for performing automatic transfer of liquid samples between a plurality of receptacles. More specifically, it is directed to a system for transferring liquid samples between a multiplicity of separate liquid receptacles, such as is required, for example, in serial dilution and chemical analysis of liquid samples in microtiter trays where each receptacle holds only about one tenth to ten milliliters of liquid. A serial dilution operation basically involves mixing a sample with successively increasing proportions of a diluent in separate receptacles to obtain a series of successively decreasing concentrations of the sample. The various sample concentrations can then be assayed to determine a particular property. For example, the sample might be a serum and the assay might be used to determine which concentration of the serum provides optimum results when reacted with a particular substance.
Initially, assay of a sample was performed manually, wherein different reagents would be mixed in different respective test tubes, for example with the aid of a syringe or pipette. This procedure consumed a considerable amount of time when a number of different assays were required. Consequently, machines for automatically or semi-automatically performing assays were developed. One example of such a machine is disclosed in commonly assigned U.S. Pat. No. 4,478,094.